> ## Documentation Index
> Fetch the complete documentation index at: https://confidence.spotify.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Analysis

> Analysis lets you analyze experiments that run outside of Confidence. For example, you can re-analyze experiments you ran before using Confidence, to gather all experiments in one place.

In Confidence, an analysis resembles an A/B test.
The main difference is that the experiment is not run in Confidence and is already ended.

An analysis is different from an A/B test in the following ways:

* No continuous monitoring of the experiment
* The treatment variants are not variants on a feature flag in Confidence
* No sample size calculator on the Design page. View the powered effect size on the Detailed results view like for A/B tests.
* You don't launch analysis instances, since the experiment is not live. Select the metrics you want and click **Calculate** to see the results.

## Analyze Optimizely Experiments in Confidence

You can analyze past or current experiments in Optimizely with Confidence.
To do so, you need to [export the decision events](https://docs.developers.optimizely.com/experimentation-data/docs/enriched-events-export)
from Optimizely to a table in your data warehouse.
A decision event is an event that Optimizely records when a visitor is exposed to an experiment.
Decision events in Optimizely correspond to assignments in Confidence.

The information Confidence requires is available in the columns:

* `experiment_id`: column with identifiers of the experiments
* `variation_id`: column with identifiers of the variants
* `visitor_id`: column with identifiers of the entities in the experiments, like users and visitors
* `timestamp`: column with timestamps of the events

Before setting up an analysis, make sure you have configured your
[data warehouse connection](/docs/warehouse-setup/bigquery).

The steps to analyze an Optimizely experiment in Confidence are:

1. [Export](https://docs.developers.optimizely.com/experimentation-data/docs/enriched-events-export)
   the [decision events](https://docs.developers.optimizely.com/experimentation-data/docs/enriched-events-data-specification#decisions-1)
   from Optimizely to a table in your data warehouse. If you want to analyze a running experiment,
   you need to schedule the export to happen at a regular cadence.
2. If you don't have one already, [create an entity](/docs/metrics/entities) in Confidence that identifies the
   entity that's recorded in the `visitor_id` column of the decision events table.
3. [Create an assignment table](/docs/metrics/assignment-tables) in Confidence that points to the decision events table.
   * Set the exposure key column to `experiment_id`.
   * Set the variant key column to `variation_id`.
   * Set the entity to the entity you created in step 2.
   * Set the entity column to `visitor_id`.
   * Set the timestamp column to `timestamp`.
   <Note type="info">
     The columns `experiment_id` and `variation_id` must be strings to be selectable
     as exposure key and variant. The type of the `visitor_id` must match the primary key type of the
     entity you created in step 2, such as a string. The `timestamp` column must be a timestamp.
   </Note>
4. Create a new analysis in Confidence.
   * Set the exposure key to the identifier of your Optimizely experiment. This identifier filters
     the decision events table to only include the events for the experiment you want to analyze based
     on the `experiment_id` column.
   * Set the analysis start date to the date the experiment started.
   * Click **Add treatment** and enter the identifier for the variant you want to add. This
     identifier should match what's in the `variation_id` column of the decision events table. You can
     add multiple variants. Set the weights to match the weights you used in Optimizely.
   * Click **Add metric** and select the entity and assignment table you created in step 2 and 3.
     Click continue.
   * Add a metric and click **Continue**.

If you don't have any metrics in Confidence, follow the steps in the metrics quickstart to
[create a fact table](/docs/how-to-guides/create-fact-table) and
[a metric](/docs/how-to-guides/create-fact-table). Use the entity you created in step 2.

## Related Resources

<CardGroup cols={2}>
  <Card title="Analyze Past Experiments" href="/docs/quickstarts/analyze-past-experiment">
    Step-by-step analysis tutorial
  </Card>

  <Card title="Create Assignment Tables" href="/docs/how-to-guides/create-assignment-table">
    Set up assignment data sources
  </Card>

  <Card title="A/B Tests" href="/docs/experiments/workflows/abtests">
    Compare with A/B tests
  </Card>
</CardGroup>